Up Alloying weld material? 1

[ggrindle]

For 2205 of other duplex stainless steels the weld and HAZ is much weaker (especially if too much heat input) than the rest of the material. This is to be used in outlet FGD ductwork.

I'm wondering if using C-276 wire for the welds would eliminate that weakness of would the HAZ extend past the area of dilution so that there would be no advantage to using a higher alloy material on the welds?

 

[metengr]

What do you mean by weaker? Corrosion resistance or mechanical properties? If your welding process is correctly established, you should weld the duplex with low heat input to avoid the formation of harmful intermetallic compounds in the base metal HAZ. The higher alloy weld deposit is for corrosion resistance to match or exceed the base material corrosion resistance.

 

[ggrindle]

By weaker I meant for corrosion resistance.

 

[EdStainless]

With the duplex grades it is not difficult to create welds that match the strength and corrosion resistance of hte base metal. The recommended fillers are very similar in chemistry to the base metal. The only difference is a slightly altered austenite/ferrite balance.

http://www.outokumpu.com/applications/weld/res.asp?selGrade1=5&selGrade2=5&cmdSearch=Search#

Using a fully austenitic filler in a duplex weld would not be good. If you allow too high of heat input the microstructural damage in the HAZ will be there regardless of what filler you use.

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[stanweld]

Using more corrosion resistant deposited weld metal often proves effective. Even after carefully controlling heat input using ER2209 filler and assuring proper inert gas shielding, excessive pitting in the weld metal occurred. Switching the filler metal to ERNiCrMo-3 eliminated pitting. We have also used superduplex filler metals in similar situations with similar beneficial results.

I would not recommend using the dissimilar weld metal based on cost and coefficient mismatch (unless operating temperature is relatively low)or you have established that increased corrosion/pitting rates of the near matching duplex deposited weld metal is occurring or will occur. In the majority of our installations similar to which you describe, adequate corrosion resistance has been obtained with the 2209 filler metal.

 

[stanweld]

grindle,
FYI
This week, I evaluated corrosion of welds in 316L pipe welded with ERNiCrMo-4, specified by the Owner to counteract high ptting rates of matching ER 316L deposited weld metal. In this case up alloying proved detrimental. Knife edge corrosion at the fusion line with through wall penetration. In some cases, up-alloying can backfire depending on the corrosive media and the galvanic mismatch.

 

[EdStainless]

The other issue is that high moly austenitics (316, 904L, 6%Mo ) all suffer a lot of segrigation when welded. Stan is on the money. You only want to up-alloy a little. Just enough so that the lean portion of the structure matches the base metal. If all of the weld is better, then you will drive gavanic attack of the HAZ.

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Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[stanweld]

grindle,
FYI
I've just reviewed the engineering requirements for welding 2205 in an FGD absorber. The engineer (well known in the power industry) requires the use of E/ER NiCrMo-3. Heat input not to exceed 30 KJ/in.